USB Attached to EX4100 connection disappears

After a period of time the external USB drive I have attached to my EX4100,
just disappears. If I detach/attach it(the USB drive), it will reappear in My Cloud.
I don’t know if there is a polling cycle that times out with inactivity or what.
I had an open case on this, which is closed now.
Just wondering if there is any one that has experienced something related
to this.

Note: I have another EX4100 at a client site. It has not lost connectivity with the external USB drive I have attached. They are identical in terms of firmware.
I am going to swap drives and see if it is the drive causing the issue.